SCP camshafts should not be confused with camshafts of the type described in DE 4419557 where the inner shaft can intentionally be moved radially relative to the outer tube into an eccentric position for the purpose of achieving variable event duration by superimposing a cyclic phase change on the phase of a cam lobe connected to both the inner shaft and the outer tube. In an SCP camshaft the inner shaft and outer tube rotate at all times about fixed substantially concentric axes.
An example of an SCP camshaft is described in U.S. Pat. No. 5,664,463. As is shown in the latter patent, the inner shafts of known SCP camshafts are supported in bushes or bearings within the outer tubes. This results in the camshafts being sensitive to component manufacturing tolerances.
In particular, the alignment of the holes in the inner shaft and those in the movable cams into which each of the connecting members is fitted is critical. If significant misalignment is present, the fitting of the connecting member will act to align the holes and this will cause the drive shaft to lock in its bearings in the outer tube of the camshaft. Variation in components due to manufacturing tolerances can therefore result in the inner shaft being unable to rotate relative to the outer tube of the camshaft. The need for the component parts of the camshaft to be made to an accurate specification increases the manufacturing cost of the camshaft.